Protect against segfault in audiorouting_test

If we don't successfully create a track/record in the test cases,
they will trigger a segfault which causes test runner issues.

Move from EXPECT to ASSERT to be defensive.

Bug: 288315540
Test: atest audiorouting_tests --iterations=100
Change-Id: I2a6527cb4e36942a6caaf731951833ceab79bb19